The present invention relates to a charge transfer recursive filter.
It is pointed out that a charge transfer filter essentially comprises:
a shift register for the transfer for electrical charges on a semiconductor substrate and covered by an insulating layer on which are provided transfer electrodes, which are arranged parallel to one another and transversely with respect to the direction of the charges. In the case of a periodic application of given potentials, these electrodes ensure the transfer of charges into the substrate from one register stage to the next.
weighting means connected to the output of the stages of the shift register, which allocate a weighting coefficient to the quantity of charges having passed through each stage.
In a recursive filter, electrical signal for reading quantities of weighted charges is again injected at the filter input after having been phase displaced by 180.degree.. This signal is generally supplied to the negative input of a differential amplifier, which receives at its positive input samples of the electrical input signal to be filtered. The output signal of the differential amplifier is applied to means ensuring the injection of charges, located at the input of the register in accordance with the charge transfer direction.
In the prior art recursive filters, the electrical output signal of the filter is constituted by the electrical signal for reading the quantities of weighted charges collected on leaving the shift register upstream of the differential amplifier.